Roller mill classifiers, which are integrated into a roller pan mill or a roller mill, e.g. in an air-swept mill or can alternatively be mounted thereon, can be constructed as static or dynamic classifiers.
Combinations of a static and a dynamic classifier are also known, which can then be referred to as a high-performance classifier.
A high-performance classifier for a roller mill is known under the name louvre centrifugal classifier. As the dynamic classifier is provided a centrifugal or ledge rotor classifier surrounded by concentric, interengaged cones of different diameters, accompanied by the formation of a classifying zone. A first classifying or sifting action is brought about by a coaxial whirling flow of the fluid passing out of the blade ring on the circumference of the grinding disk and this brings about a first coarse material separation in a marginal zone. An advantageous second classifying or sifting action is achieved by the louvre cones, in that the upwardly flowing fluid-grinding material mixture is exposed to flow deflections with an upward and downward flow and subsequently a radial flow, so that a second coarse material fraction is separated. This is followed by a sifting on the concentric, interengaged louvre cones, which function in the same way as a static centrifugal classifier and remove a third coarse material fraction. A further classifying action takes place during the downward movement of the grinding material-fluid flow, so that a considerable proportion of the coarse material is removed before the dynamic classification process is performed in the ledge rotor.
A further high-performance classifier is described in ZKG, vol. 46, 1993, No. 8, pp 444 to 450, FIG. 7. This classifier has a cylindrical ledge rotor and a concentrically arranged guide blade ring. A very effective tangential flow is to be produced between the static distributor and the ledge rotor, so that the coarse particles do not reach the rotor. The disadvantages are an increased pressure loss and increasing wear to the guide blades, particularly in the case of high particle concentrations.
However, as opposed to this, louvre centrifugal classifiers in operation have a relatively low wear and also a low pressure loss. However, it is disadvantageous that a rigid construction of the louvre is prejudical to an optimization of the process parameters through the static distributor and that an adaption and optimization is only possible in the field of dynamic classifying, e.g. with the aid of the rotor speed.